Wednesday, January 2, 2013

Choosing a UAV Robotic Platform for Research

So, I've been planning to look into robotics for a long time, not the least because it's closely related to my research field, evolutionary algorithms and neural networks, especially for control applications. I've done some hardware platform experiments with Arduino, but I haven't had time to do much beyond that yet. But I plan to, at least make basic motor control, PID control, balancing experiments, etc. All that just requires a bit too much tinkering with mechanics and I'm not so interested about that. I want to have the mechanics more or less ready, or at most build them from lego-style components, and concentrate on the control software. I am a software person, after all.

UAVs are, in many respects, easier than walking or wheeled things. You can concentrate on sensors, vision, navigation, and planning, instead of working years on problems like trying to climb over a branch.

The three main platforms that I've found are:

  • Arducopter
  • AscTec Hummingbird/Autopilot
  • Parrot AR.Drone 2.0

Let's look into those.

Arducopter

The Arducopter is quadrocopter with an Arduino-based control board. I'm familiar with Arduino, how to communicate with it, and how to hook sensors to it, so development would be more or less easy. The hardware is highly modifiable and it has a strong community.

The downside is that it is a bit expensive to get started with. A basic kit is around 400 €, so it would be affordable, but the basic kit is very basic. A manual 2.4 GHz remote controller would be highly useful, as well as a remote camera, but they are rather expensive. There would also be a lot of initial work to get it all assembled, configured, and ready to fly.

AscTec Hummingbird

The AscTec Hummingbird has been used in UAV robotics research, most famously by the GRASP laboratory at the University of Pennsylvania, who have used them to create quite amazing flight maneuvers and swarm behaviour.

The AscTec UAVs can be remote controlled with the AscTec SDK, which communicates with the UAV using ZigBee, a commonly used serial radio chip. I've used those with Arduino, they are dumb-easy to use at the simplest. One problem is that there apparently is no on-board API.

While claimed to be the top-of-the-line research UAVs at the moment, they are horribly expensive, reportedly starting from around $4000 for barebones configuration and around 15000 € for a full-featured one, whatever that means. I have not even been able to find a shop that sells them and the manufacturer provides very little details, so it's hard to say much about them. In any case, can't afford one.

Parrot AR.Drone 2.0

The Parrot AR.Drone 2.0 is probably the most well-productized UAV at the moment. It is sold in fully working condition and can be controlled with an Android or iOS device, such as a phone or a tablet, using a WLAN link with the device. The link is specified to have a range of around 50 meters in optimal conditions, so the device is clearly just for close use, especially as it has no built-in autonomous flight.

The AR.Drone includes a 720p video camera through the WLAN link, so you can navigate the UAV using the video link. It also has a separate small video camera pointing directly downward for ground speed measurement.

The vehicle has a gyroscope, accelerometer, magnetometer, barometer, ultrasound sensors, and the two cameras for navigation. That's more than enough for most experimental purposes. No GPS though, so long-distance autonomous navigation is not so easy.

The payload capacity is not even mentioned and the manufacturer even warns that additional payload may affect flight stability. The battery lasts just for some 12 minutes.

Most importantly, the manufacturer provides a remote control API for Linux, Mac, and Windows. This openness has allowed the UAV to have been used for research, which would also be my purpose. Also, the on-board flight controller is a Linux-based embedded computer. It has a 1 GHz ARM processor and 1 GB RAM, plus a DSP for video, and the WLAN, so it's actually much more efficient than a Raspberry. You can log into the system using Telnet, probably even during flight. One big question is, are also the in-controller APIs open, which would be essential for developing autonomous functions that would work without the WLAN control loop.

The price for the AR.Drone 2.0 is just 300 €, plus some 30 € for a spare battery and 40 € for the indoor protective frame. All the parts are sold also as replacement parts, although not very cheap. That could also mean that it breaks very easily...

While apparently marketed foremost as a toy for kids (of rich parents), the AR.Drone appears to have all the features of an excellent research platform. It's just great if they get their main income from the consumer market to bring the prices down.

Conclusions

The AscTec Hummingbird is clearly out of my resources at the moment. The Arducopter would be interesting and probably the most flexible solution. However, as I'm just entering the UAV hobby/research, it's best to buy some cheap entry-level solution that still allows some flexibility. Apparently, the AR.Drone can do all the basic things I need right out of the Box at a great price.

1 comment:

戴晓天 said...

Thanks for this article. I'm also looking for a properly quadcopter platform.